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Autoignition resistance for HC
• n-alkanes - have very low ON, the more molecular weight the low ON • Isoalkanes – branching of chains enhances an ON • The highest ON have isoalkanes with tertiary and quaternary carbons • Naphtens – cyclopentane and cycloheptane have high ON. The side chains decrease an ON. • The longer side chain the lower ON • Arenas – the highest octane components of gasolines, but its content must be under 50% by mass. • Overly aromatized fuel enhances of combustion point and increases a tool deterioration Additives • ways to improve the octane number of gasoline • change the composition of gasoline (difficult and expensive), – add additives that destroy peroxides and prevent knock effects. • The additive added in a very small amount in gasoline allows the increase of the octane number by about 5 – 10 units. Oil Classifications l <ll < lll - sulfur content T1 >T2 > T3 - light fractions with b.r. under 3500C content M1 >M2 >M3 – potential lubricating oils content И1 >И2 >И3 >И4 – viscosity index П1 < П2 < П3 - paraffin wax content Chemical classification
In according to density
• In according to viscosity mm2/s: • Low viscous 0÷40 • Viscous 40÷80 • High viscous >80 • Jetybai Oil • Sulfur content - 0,1% mass: • Content light fractions under 3500С %mass – 41,2 • Potential content of lubricating oils %–34,8 • Viscosity index – 95 • Paraffin wax, % mass. - 23,4 • Gasoline fraction of Tengiz oil • (gasoline (b.r. 65-1800С) • Sulfur content 0,16% • Octane Number -39 • Density d204 =0,7557 • Arenas - 15 % • Cycloalkanes – 29% • Alkanes -56% Natural Gases • Raw natural gas comes from three types of wells: • oil wells, • gas wells, • condensate wells.
• 1. Non-associated • 2. Associated • 3. Oil Refinery Gases Non-Associated Gases • - 98-99% СН4, other - С3Н8, С4Н10, С5Н12 • Impurities: H2S, CO2, CS2, COS, RSH, N2 sometimes – He, Ar, also water. • All components – saturated HC, (unsaturated HC do not present). Associated Gases • Natural gases which are extracted along with crude oil • Besides methane - C2H6, C3H8, C4H10 and more heaver HC • Also are present – H2S and not combustible components – N2, CO2, He, Ar • Percentage of С 3Н 8-С 4Н 10 are bigger then in natural gases and varies from 30 to 70%. • All HC saturated • Sometimes gas can be dissolved in crude oil and it can be extracted just together with oil. Typical Composition of Natural Gas | |||||
| Methane | CH4 | 70-9 8% | ||||
| Ethane | C2H6 | 0-20% | ||||
| Propane | C3H8 | |||||
| Butane | C4H10 | |||||
| Carbon Dioxide | CO2 | 0-8% | ||||
| Oxygen | O2 | 0-0.2% | ||||
| Nitrogen | N2 | 0-5% | ||||
| Hydrogen sulphide | H2S | 0-5% | ||||
| Rare gases | A, He, Ne, Xe | trace | ||||
• Gaseous factor – amount of gases in m3, per 1 t of extracted crude oil.
• «Wet Gases» –consist heavy HC above 50 g/m3.
• «Dry Gases» – mainly methane, under 50 g/m3 heavy HC.
• Basically pure gases wells (before 98% CH4)
Gas condensate
• condensate wells produce free natural gas along with a semi-liquid hydrocarbon condensate.
• Gas condensate – is a mixture of gaseous hydrocarbons with light liquid hydrocarbons (C5-C12) which are found in vaporized state.
• Most condensates are composed of saturated hydrocarbons in the light gasoline range (butane, pentane and hexane).
• Gas produced from a field containing significant quantities of condensate is characterized as wet gas.
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• Natural Gas Liquids (NGL) - liquid light hydrocarbons
• Liquefied Petroleum Gas (LPG) - gas is liquefied under very low T and high P
Gases are used for
• producing energy (gas turbine engine)
• producing motor fuel (fueling)
• as a source for petrochemistry
• in oil and gas refinery as fuel gases
• heating homes,
• heating water,
• cooking and refrigerating
Methods for gases separation
• 1. Condensation
• 2. Compression
• 3. Absorption
• 4. Adsorption
• 5. Rectification
Condensation
• Gas is converted into two phase system – liquid-gas
• Refriagents - air, water, ammonium, freon,, gases – propane and ethane
• About 70% of ethane and 90% of propane is liquefied
Oil Emulsions
• Dispersion – раздробленность
• Dispersed system – mixture where one substance is dispersed evenly throughout another
• And dispersed substance is suspended in the mixture
• Dispersed system is a dispersion of one substance (dispersed phase) in the another (dispersion medium)
• dispersed phase (or internal phase) – dispersed particles
• continuous phase (or dispersion medium)
• Colloidal particles – aggregates of molecules
• Particle size ranges from 5 to 1000 nm.
• Coagulation – cohesion of colloidal particles in to more bigger aggregates under gravity forces
• Sedimentation - falling down to the bottom under gravity
Emulsion – is a system of two immiscible (unblendable) liquids where one liquid is
evenly dispersed in the another as a droplets (globules)
• Surface tension is measured as the energy required to increase the surface area of a liquid by a unit of area.
• The surface tension of a liquid results from an imbalance of intermolecular attractive forces, the cohesive forces between molecules
• Substances which decrease the surface tension of liquid – surface active substances
• The less surface tension the less liquid resists to increasing their surface the either to cohere of droplets
• Emulsifiers – surfactants that promote emulsion formation and influence the ability to form an emulsion
• Demulsifies – surfactants that decrease the emulsion’s stability
Crude oil consist of:
- associated gas - 50-100 m3/t,
- reservoir water 200-300 kg/t,
- mineral salts under 35%
- other impurities (sand, clay etc.)
When crude oil is extracted
• Stable oil emulsions can be formed because of there is intensive blend of crude oil and reservoir water
• The stability of oil emulsion is provided by formation of very stable adsorptive layer around the colloidal particle
• Hydrophilic: oil-in-water - is evenly dispersed in water
• Hydrophobic: water-in-oil – is evenly dispersed in gasoline or in crude oil
• Over 95% of the crude oil emulsions - are hydrophobic emultions.
• The presence of water in crude oils is caused by:
• Natural mixing with oils during their migration
• Washing of tubing for scale dissolving
• Washing of oil for salts dissolving
• Seawater contamination during marine transportation.
• Not all emulsions are equal in stability. There are several factors that contribute to the stability of an emulsion:
• Size of Dispersed Water Drops
• Viscosity and Density of Crude Oil.
• Salinity of Brine.
• Age of Emulsions.
Emulsifies
• Oil surfactants - sulfur contain compounds, resins, asphaltens, salts and others
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• They adsorb on the surface of the droplet and form the protective layer which covers the droplet with a preserving layer thereby stabilizing the droplet.
